How do we know this is alien? Because the liars in government told us?

Quoting: Defragthis

sighpay attentionthe object was seen as a result of attention shifted to the sky by a Russian satellite, which didn't attain permanent orbit being too low. The bogey was in a Polar orbit which requires more thruster than any Earth power had.

so - we see larger and higher than mans ability. The Easter Bunny or aliens, your pick.